1. Field of the Invention
The present invention relates to a method of forming an annular member of a torque converter, and in particular to a method of forming the annular member by bending a flat plate material or blank into an annular shape.
2. Description of the Background Art
A torque converter is a device which includes three kinds of vane wheels (impeller, turbine and stator) and is operable to transmit a torque through a working fluid filling an interior thereof. The impeller is fixed to a front cover coupled to an input rotary member, and transmits a torque to an output member through the working fluid flowing from the impeller to the turbine. A lockup damper included in the torque converter is disposed between the turbine and the front cover, and is operable to mechanically couple the front cover and the turbine together and thereby transmit torque from the front cover directly to the output member. The lockup damper includes a piston to be pressed against the front cover, a retaining plate fixed to the piston, torsion springs carried by the retaining plate and a driven plate which is elastically coupled in the rotating direction to the piston through the torsion springs. The driven plate is fixed to the turbine coupled to the output rotary member.
The torque converter is a rotating mechanism, and many components thereof are formed with an annular shape. For example, a driven plate 20 shown in FIG. 1 is an annular member, and includes an annular fixing portion 20b, which has a form extending along the outer peripheral surface of the turbine 5, and a plurality of claws 20a extending from the fixing portion 20b toward an engine (not shown). In the prior art, the annular member is formed by deforming a circular plate, which is first prepared by cutting an annular blank and forming holes at an inner peripheral portion thereof.
However, the overall yield from raw materials used to produce such annular blanks are low if the driven plate 20 and other annular members are produced from annular blanks having an outer circumference that corresponds to the fixing portion 20b or the like, where such annular blanks are prepared by cutting an annular shaped blank from flat materials. In other words, cutting annular shaped blanks from flat raw materials is an inefficient use of materials because there is alot of waste or scrap material left over after cutting.